I have had the privilege of using an SWR Analyzer to check my antenna when tuning-up,etc on HF...but now that I no longer have access to it nor the money to buy one I was wondering why I couldn't use one of my RF Signal Generators and an SWR Meter as a non-portable SWR Analyzer.
So I hooked them up and was not able to accomplish what I had hoped?
So that brings me here to ask all of you,what am I missing? What do I need to make this work?
Any help with this would be greatly Appreciated
# I have no idea, I just wanted to say "Dear Curious"
# # # and sign,
# # # # # # # # Yours truly, "Dazed and Confused". #
Actually, my not-so-educated guess is that your signal generator (test bench instrument I'm guessing) doesn't produce enough power to drive the SWR meter. But that is a tough call not knowing the kind of signal generator it is or what it is capable of. An SWR meter generally requires a few watts of power to deflect the coil and movement. How many watts is your generator producing? And why would your radio not be an adequate signal generator anyway?
BTW, no need to use a stage name. We're all hams here! What's your call?
My favorite mode? Morse, of course.
Simple answer. #An "analyzer" tells you the characteristic of the reactance that is present #( inductive, capacitive, resistive, how much of each ) where an SWR meter only tells you that the system is NOT presenting a 50 ohm non-reactive match to the source. #
Actually for years Palomar#Engineering, has manufactured Noise Bridges. # I see that MFJ has these devices too. #See this LINKY
A lot less expensive than an analyzer, and almost as useful !
This link to an earlier QRZ string is even more interesting ! #
Hope this helps !
Ham Radio, Amateur Astronomy, and Model Airplanes - what better way to spend some time!
No time is ever wasted that is spent LEARNING something !
Jim, it sounds to me like he isn't so much interested in measuring the reactance of the antenna as he is looking for a way to check SWR without transmitting a carrier. I have a tektronics signal generator at work that I've used maybe ONE TIME in my career, so my experience is quite low, but I do not think it puts out much more than a few mV's, not enough to drive a circuit of any consequence without some sort of amplification...would you agree with this?
Originally Posted by [b
My favorite mode? Morse, of course.
I am thinking that he could build a small millawatt meter and use a return loss bridge with his sig gen to do what he wants, but I also think that a standard sig gen would not be able to get very accurite frequency read out unless it was the digital type or dds generator.
A decent signal generator should be able to get into the "ballpark," and relatively stable; the exact frequency can be checked with a receiver or frequency counter, and again, if halfway decent, it shouldn't change frequency by more than a few hundred Hz for a short period of a few minutes, and for antenna testing, even a bit of frequency "wobble" on the order of a few kHz shouldn't matter much. (Certainly, the stability of a signal generator should be at least as good as the MFJ Analyzers...)
The problem with using any type of common SWR bridge will be sensitivity; but amplifying the signal that normally goes to the meter might provide a decent reading; the MJF and other analyzers operate on much the same principle.
But whether you use an analyzer, a signal generator, OR a transmitter to check the SWR, you ARE generating and applying an RF signal, and if the item being tested is an antenna, a signal WILL be radiated.
"O tempora, O mores" as Cicero lamented.
The analyser is king today; it's sometimes forgotten that there are other ways to determine whether a transmitter is "matched" to an antenna.
Some (but not all) of the necessary instruments are listed in other posts; SWR meters, RF bridges, RLBs, noise bridges etc have been fashionable within living memory whilst knowledge of older devices is being lost.
For basic antenna adjustment I like the noise bridge. I have three of them; an old Omega-T (see AG3Y's link), a mint Palomar one and a homebrew one which, due to considerable effort in design & construction, is my "best" one.
The Palomars often appear on ebay at realistic prices; this realism is due, no doubt, to their unfashionability.
A receiver is required; I use a Sony ICF-7600 but any of the el-cheapo portables with appropriate shortwave bands and, preferably, digital display (although an analog dial could be calibrated against a sig-gen or other source) should do. Only AM capability is required.
This will make a useful portable test setup that can be taken outside or used on the bench.
For a basic but effective analyser (two designs, in fact) look here;
I have built both of these and each works well.
Even though the A$ is up against the US$ the purchase of the HF kit might still be worthwhile.
My favorite set up is a sig gen (any freq of interest am'd at 1 KHz (sinusoidal or even square waveform am)), return loss bridge, diode detector and an old hp415B SWR indictator. I can also substitute an impedance bridge for the RLB to measure the actual Z, put that on the Smith Chart and determine all from that. My brigdes (RLB and Z)are homebrewed as are VK2TL's or similar. I have acquired some commercial bridges now as well (GR and HP). The basic RLB and diode detectors are very easy build and are in the ARRL HB's. I have obtained 3 hp415 SWR indictors all for less than $20 USD each at hamfests. The E version is the latest and transistorized. The only thing that might not be cheap is the sig gen which, however, can be used for many things and is great to have. With all of this junk and a few other minor gadgets, I can measure IL (insertion loss), RL(return loss equatable to SWR) and impedance from 100 kHz to 2.8 GHz nearly continuously (and from 20 Hz to 20KHz with a GR 1608). In any case, this has been a big part of amateur radio for me...much more than operating. 73, Pete
UAQ's setup is one of the forgotten techniques I referred-to.
Use of the 415 SWR meter was common in microwave work until the advent of the microwave VNA and other devices.
I still have two slotted lines (HP 809C & Alford 3300) and a 415E.
vk2til de wb2uaq
Also have a slotted line (HP805, 500 MHz-4GHz) and a GR1602 Admittance meter (40 MHz - 1500 MHz). The GR1602 is interesting but needs a lot of support stuff and uses the famous GR874 connectors. I also use the HP415 as a null meter for the 1602. The 415 with a diode detector and sig gen is great for measuring the loss of filters and transmission lines and many other devices with an input and an output. I also use it as a field strength meter with its log scales. It is very useful and the log scales are very accurate. I visited a standards lab and it was used to test rf attenuators by a substitution method with a standard attenuator.
73 again, Pete